Abstract

Based upon superconducting gravimeter and seismometer records, the autoregressive method is used to determine the frequencies and quality factors of five spheroidal modes: four fundamental modes 0S0, 0S2, 0S3, 0S4 and one
higher mode 2S1. The data used are 113 records from five major earthquakes (Sumatra-Andaman earthquake 2004, Chile earthquake 2010, Tohoku earthquake 2011, Achet earthquake 2012 and Illapel earthquake 2015) with the moment magnitude above 8 recorded at 46 stations worldwide. Estimated weighted average values of the eigenfrequencies and the quality factors of the mode’s singlets are very close to the results of the previous studies as well as the PREM predictions. However, some results show deviations from theoretical PREM values, supporting the fact that this model is not appropriate to explain all processes in the Earth, because of Earth’s complexity.
Additionally, standard deviation estimated by the bootstrap method are realistic and consistent. While this autoregressive method gave satisfactory results, one should be aware of the fact that this method relies heavily on the high quality data, because non-linearity destroys autoregressive nature of time series and hence introduces bias in the estimate.